Proportional-integral (PI) feedback control can be used to regulate disturbances and achieve desired setpoints in HVAC systems. One example of a component in an HVAC system that can use such PI feedback control is a fan coil unit (FCU), which can regulate fan speed, cooling/heating medium flow, and/or other variables to meet desired temperature of a zone. The PI parameters, proportional gain and integral time can, however, be difficult to determine and pre-set, prior to commissioning of the HVAC system. Further, when implemented, such HVAC systems and components can be affected by a variety of time-dependent variables that often make a single set of PI parameters unsuitable for indefinite use. As a result, PI parameter re-tuning is often desired, allowing the controller to respond to changes in the characteristics of the system.
To provide such dynamic system control, the HVAC system controllers may be re-tuned while online. Tuning may be manual, proceeding by trial-and-error, or may be automatic. Manual tuning is often time consuming and can lead to sub-optimal results, for example, by introducing human error. Further, automatic tuning or “autotuning” is frequently inaccurate and/or unreliable. If a process disturbance occurs during such autotuning, the controller can erroneously set the PI parameters as if the transitory disturbance was part of the system cause-effect response. Further, system models, often used to estimate the tuning parameters from information measured in the system, can be difficult to identify online.
What is needed are systems and methods for autotuning an HVAC system controller.